Generally, a lid mounting device of the type has a main body to be attached to a case, and a lid supporting member rotatable around a pin provided at one end of the main body. When mounting a lid to a case, a pair of such lid mounting devices are fixed to the case in such a way that their main bodies are spaced from each other and pins thereof are positioned in alignment, and then one end of the lid is clamped to lid supporting members.
However, it is difficult to fix the main bodies of the both lid mounting devices to the case so that their pins may be positioned in alignment, and in reality some mounting error is inevitable. If the mounting error is greater than tolerable, it is impossible to clamp one end of the lid to the lid supporting members, or if clamping could be done, some unreasonable force (e.g., shear force) may be exerted on the lid during opening and/or closing movement of the lid, thus resulting in lid breakage.